A digital interpolation shaping filter based on doppler compensation for spread spectrum communication systems

Abstract

The application discloses a kind of digital interpolation shaping filters based on doppler compensation of spread spectrum communication system.For reducing the interference of Doppler effect, spread spectrum communication system artificially changes the code rate of spread spectrum code in transmitting end, so that the receiving code rate after the influence of Doppler channel is close to the system design code rate.In order to save hardware resources, meet the shaping filter demand that the interpolation multiple will also change after the change of spread spectrum code rate in transmitting end, this paper gives a kind of filter structure.Firstly, when the effective spread spectrum signal comes, the filter will lock the spread spectrum signal into the corresponding numbered latch according to the value of counter.Then, when the latch locks the new signal, start coefficient memory, and output the filter coefficient in turn according to clock sequence.Finally, multiply the latch with the same number and the output of coefficient memory and add them to get the output of filter.

Description

Technical Field

[0001] Communication anti-interference technology Background Technology

[0002] Spread spectrum communication is a communication method that transmits information by widening the spectrum of a signal carrying information. The bandwidth of the transmitted signal is mainly determined by the spreading function and is independent of the information signal. Shannon pointed out that, under Gaussian white noise interference, in channels with limited average power, the optimal signal for effective and reliable communication should have the statistical characteristics of white noise. The spreading function using pseudo-noise codes closely approximates the statistical characteristics of white noise, thus spread spectrum communication systems have strong resistance to man-made interference, narrowband interference, and multipath interference. Therefore, spread spectrum communication systems not only occupy an important position in military communications but are also increasingly widely used in civilian communications.

[0003] When spread spectrum communication systems are applied to inter-satellite links, the high-speed relative motion between satellites can cause significant Doppler shifts, affecting system performance requirements and increasing acquisition resource consumption. To reduce the impact of the Doppler effect, the communication system first transmits a fixed signal to estimate the channel conditions, and then artificially changes the code rate of the spreading code at the transmitting end so that the code rate after the Doppler effect is close to the system's design code rate.

[0004] In spread spectrum communication systems, when the code rate is artificially altered at the transmitter, the signal code rate and sampling clock no longer maintain a fixed multiple relationship, making it impossible to use shaping filters with fixed interpolation multiples. Furthermore, interpolation shaping filters generally require a large order, and ordinary filters need multipliers and adders of the same order, significantly increasing hardware resource consumption. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing filters and provide an interpolation shaping filter based on Doppler compensation in spread spectrum communication systems. This filter has a simple structure, does not require excessive resource overhead, and achieves interpolation shaping filtering processing where changes in the code rate caused by Doppler compensation in spread spectrum communication systems also result in changes in the interpolation factor.

[0006] The technical solution of this invention is: a digital interpolation shaping filter method based on Doppler compensation in a spread spectrum communication system, comprising:

[0007] Based on the Doppler compensation range of the transmitter of the spread spectrum communication system, determine the number of adders and multipliers required for filtering according to the maximum code rate;

[0008] The variable-rate spread spectrum signal at the filter input is counted, and the input code signal is allocated to the corresponding latch based on the count value.

[0009] The output of the coefficient memory is determined based on whether the latch has latched a valid signal, and the latch is released based on the state of the coefficient memory.

[0010] Multiply the outputs of latches and coefficient memories with the same number, and then add all the results together to obtain the interpolated filter output.

[0011] Preferably, based on the Doppler compensation range of the spread spectrum communication system transmitter, the required number of adders and multipliers is determined according to the maximum code rate as follows:

[0012] If the maximum spreading code rate after compensation within the Doppler compensation range at the transmitter is Rc, the DA sampling rate at the transmitter is Rs, and the order of the shaping filter is M, then... Determine N latches, memory, multipliers, and N-1 adders.

[0013] Preferably, the step of determining the output result of the coefficient memory based on whether the latch has latched a valid signal, and releasing the latch based on the state of the coefficient memory, includes:

[0014] When the latch is not latching a signal, the output of the coefficient memory remains off;

[0015] When the latch latches a new signal, the coefficient memory is activated, and the coefficient parameters are output sequentially according to the sampling rate Rs.

[0016] Once all filter coefficients have been output, the coefficient memory shuts down its output and releases the corresponding latches.

[0017] A digital interpolation shaping filter based on Doppler compensation in a spread spectrum communication system, implemented according to the method, includes a counter, a signal distribution module, N latches, N memories, N multipliers, and N-1 adders; the output of one coefficient memory and one latch is connected to one multiplier, forming a fixed cooperative relationship between the coefficient memory, latches, and multipliers;

[0018] The counter counts the input variable-rate spread spectrum signal and allocates the input code signal to the corresponding latch based on the count value.

[0019] The latch controls whether the coefficient memory outputs based on whether a valid signal is latched. When a new signal is latched, the coefficient memory is activated and the latched new signal is sent to the corresponding multiplier.

[0020] The coefficient memory outputs the pre-stored filter coefficient parameters to the corresponding multiplier under the control of the latch;

[0021] The multiplier performs a multiplication operation on the outputs of the latch and the coefficient memory, and outputs the result to the corresponding adder.

[0022] The N-1 adders sum the results of the N multipliers to obtain the interpolated filter output.

[0023] Preferred,

[0024] Where Rc is the maximum spreading code rate after compensation within the Doppler compensation range of the transmitter, Rs is the DA sampling rate of the transmitter, and M is the order of the shaping filter.

[0025] Preferably, the coefficient memory stores the filter's coefficient parameters and can be replaced as needed.

[0026] Preferably, when the latch does not latch a signal, the output of the coefficient memory remains closed. When the latch latches a new signal, the coefficient memory is activated, and the coefficient parameters are output sequentially according to the sampling rate Rs. After all the filter coefficients have been output, the coefficient memory closes its output and releases the corresponding latch.

[0027] A digital transmitter for a spread spectrum communication system, wherein the digital interpolation shaping filter described above is used for shaping filtering in the transmitter;

[0028] The transmitter adjusts the spread spectrum clock to change the code rate of the spread spectrum code, so that the received code rate after the Doppler channel influence is within a preset difference range from the system design code rate.

[0029] The digital interpolation shaping filter is designed according to the maximum code rate among the received code rates after the influence of the Doppler channel, and performs shaping filtering on the Doppler-compensated interpolated signal; then it is sent to the DA transmitter after up-conversion.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] To address the challenge of interpolation shaping filtering under Doppler compensation in spread spectrum communication systems, this patent proposes an interpolation shaping filter suitable for Doppler compensation. Engineering testing has verified that this filter can meet the requirements of interpolation shaping filtering under Doppler compensation in spread spectrum communication systems while consuming minimal resources.

[0032] This filter is implemented using a purely digital method, which is simple to implement, consumes few resources, is easy to implement on satellites, and has a strong market competitiveness.

[0033] (1) Digital methods are used to implement interpolation shaping filtering of spread spectrum signals, eliminating the need for front-end interpolation followed by filtering, thereby significantly reducing the design difficulty and manufacturing cost of spread spectrum transmitters;

[0034] (2) The interpolation factor and the filter coefficient can be replaced, which means that compared with the traditional shaping filter, the shaping filter designed by this method can be applied to the case where the spreading code rate changes within a certain range under Doppler compensation, so that the whole has stronger anti-Doppler performance.

[0035] (3) It fully considers the influence of invalid signals introduced by filter calculation after signal interpolation, and can achieve stable and reliable operation of the filter with very few multiplier and adder resources.

[0036] (4) The method has a clear functional structure, each part is relatively independent, and it is simple to implement. It does not introduce additional processing complexity, increases the flexibility of system use, meets different usage requirements, and facilitates the modular design and debugging of filters. Attached Figure Description

[0037] Figure 1 This is a flowchart of the digital transmitter processing in the spread spectrum communication system of the present invention;

[0038] Figure 2 This is a structural diagram of the digital interpolation shaping filter in this invention; Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments:

[0040] The data source, after encoding and modulation, yields a symbol width of T. d The digital signal d(n) and the symbol width T c The local spreading code c(n) is correlated to obtain the spreading signal k(n) = d(n)c(n), and after interpolation, the signal s(n) = [k(n), 0, 0, ..., 0]. The transmitter controls the symbol width T of the local spreading code by adjusting the spreading clock. c This allows for Doppler compensation. After shaping filtering, s(n) yields the signal y(n) = ∑s(n)h(τ-n), which is then up-converted and sent to the DA transmitter.

[0041] In digital transmitters, FIR filters are used for shaping. Assuming the filter order is M, a typical filter structure requires M multipliers and M-1 adders. Furthermore, ordinary filters can only perform interpolation with a fixed multiple, which cannot meet the requirement that the interpolation multiple can also be variable due to changes in code rate under Doppler compensation.

[0042] To reduce Doppler interference, spread spectrum communication systems artificially alter the code rate of the spreading code at the transmitting end, ensuring that the received code rate after the Doppler channel effect is close to the system's design code rate. To conserve multiplier and adder resources and meet the shaping filter requirement where the interpolation factor changes after the spreading code rate is altered at the transmitting end, this paper presents a filter structure. The design and implementation scheme follows these steps:

[0043] (1) The transmitting end determines the filter parameters and hardware resources based on the Doppler compensation range. After determining the maximum spreading code rate and sampling rate, the order of the filter and the required adder and multiplier resources can be determined.

[0044] (2) Count the spread spectrum signals entering the filter and assign the signals to the corresponding latches according to the count values.

[0045] (3) When the latch latches a new signal, the coefficient memory is started and the coefficient parameters are output sequentially in clock order.

[0046] (4) The output signals of all latches and coefficient memory are processed by multipliers and adders to obtain the interpolated and filtered output signals.

[0047] The operating steps of a digital interpolation shaping filter are as follows:

[0048] 1) Determining filter resources

[0049] Resources are determined based on the Doppler compensation range of the transmitter. Assuming the maximum spreading code rate after compensation is Rc, the sampling rate at the transmitter is Rs, and the order of the shaping filter is M, then... It can be implemented with just N multipliers and N-1 adders.

[0050] 2) Filter input

[0051] The filter operates under the interpolated sampling clock. When the spread spectrum signal arrives, the filter counts the input code signal and latches the code signal into the corresponding latch according to the current count value.

[0052] 3) Filter operation

[0053] The coefficient memory stores the shaped filter coefficients and can be replaced as needed. When the latch is not latching a signal, the coefficient memory output remains closed. When a new signal is latched, the coefficient memory is activated, and the coefficient parameters are output sequentially in clock order. Once all filter coefficients have been output, the coefficient memory closes its output and releases the corresponding latch.

[0054] 4) Filter output

[0055] Multiplying the output of the latches with the same number by the output of the coefficient memory, and then adding all the multipliers together, yields the output signal after interpolation shaping and filtering.

[0056] Figure 2 A digital interpolation shaping filter based on Doppler compensation in a spread spectrum communication system is presented, including a counter, a signal distribution module, N latches, N memories, N multipliers, and N-1 adders; the output of one coefficient memory and one latch is connected to one multiplier, forming a fixed cooperative relationship between the coefficient memory, latches, and multipliers;

[0057] The counter counts the input variable-rate spread spectrum signal and allocates the input code signal to the corresponding latch based on the count value.

[0058] The latch controls whether the coefficient memory outputs based on whether a valid signal is latched. When a new signal is latched, the coefficient memory is activated and the latched new signal is sent to the corresponding multiplier.

[0059] The coefficient memory outputs the pre-stored filter coefficient parameters to the corresponding multiplier under the control of the latch;

[0060] The multiplier performs a multiplication operation on the outputs of the latch and the coefficient memory, and outputs the result to the corresponding adder.

[0061] The N-1 adders sum the results of the N multipliers to obtain the interpolated filter output.

[0062] Figure 1 A digital transmitter for a spread spectrum communication system is provided, wherein the transmitter employs... Figure 2 The digital interpolation shaping filter in the middle is used for shaping filtering;

[0063] The transmitter adjusts the spread spectrum clock to change the code rate of the spread spectrum code, so that the received code rate after the influence of the Doppler channel is close to the system design code rate, that is, the difference between the two is within a preset difference range.

[0064] The digital interpolation shaping filter is designed according to the maximum code rate among the received code rates after the influence of the Doppler channel, and performs shaping filtering on the Doppler-compensated interpolated signal; then it is sent to the DA transmitter after up-conversion.

[0065] The parts of this invention not described in detail are well known to those skilled in the art.

Claims

1. A digital interpolation shaping filter method based on Doppler compensation in a spread spectrum communication system, characterized in that: Based on the Doppler compensation range of the spread spectrum communication system's transmitter, determine the number of adders and multipliers required for filtering according to the maximum code rate; The variable-rate spread spectrum signal at the filter input is counted, and the input code signal is allocated to the corresponding latch based on the count value. The output of the coefficient memory is determined based on whether the latch has latched a valid signal, and the latch is released based on the state of the coefficient memory. Multiply the outputs of latches and coefficient memories with the same number, and then add all the results together to obtain the interpolated filter output.

2. The method according to claim 1, characterized in that: Based on the Doppler compensation range of the spread spectrum communication system transmitter, the required number of adders and multipliers is determined according to the maximum code rate as follows: The maximum spreading code rate after compensation within the Doppler compensation range of the transmitter is Rc The transmitter's DA sampling rate is Rs The order of the shaping filter is M ,but ,Sure N A latch, N Coefficient memory, N A multiplier and N -1 adder.

3. The method according to claim 2, characterized in that: The step of determining the output result of the coefficient memory based on whether the latch has latched a valid signal, and releasing the latch based on the state of the coefficient memory, includes: When the latch is not latching a signal, the output of the coefficient memory remains off; When the latch latches a new signal, the coefficient memory is activated, and the coefficient parameters are stored according to the sampling rate. Rs Output sequentially; Once all filter coefficients have been output, the coefficient memory shuts down its output and releases the corresponding latches.

4. A digital interpolation shaping filter based on Doppler compensation in a spread spectrum communication system, implemented according to claim 1, characterized in that: Includes counters, signal distribution modules, N A latch, N Coefficient memory, N A multiplier and N -1 adder; The output of a coefficient memory and a latch is connected to a multiplier, forming a fixed cooperative relationship between the coefficient memory, latch, and multiplier; The counter counts the input variable-rate spread spectrum signal and allocates the input code signal to the corresponding latch based on the count value. The latch controls whether the coefficient memory outputs based on whether a valid signal is latched. When a new signal is latched, the coefficient memory is activated and the latched new signal is sent to the corresponding multiplier. The coefficient memory outputs the pre-stored filter coefficient parameters to the corresponding multiplier under the control of the latch; The multiplier performs a multiplication operation on the outputs of the latch and the coefficient memory, and outputs the result to the corresponding adder. N -1 adder will N The results of the multipliers are added together to obtain the interpolated filter output.

5. The digital interpolation shaping filter according to claim 4, characterized in that: in, Rc This represents the maximum spreading code rate after compensation within the Doppler compensation range of the transmitter. Rs The DA sampling rate at the transmitter. M This represents the order of the shaping filter.

6. The digital interpolation shaping filter according to claim 4, characterized in that: The coefficient memory stores the filter's coefficient parameters and can be replaced as needed.

7. The digital interpolation shaping filter according to claim 4, characterized in that: When the latch is not latching a signal, the coefficient memory output remains off. When the latch latches a new signal, the coefficient memory is activated, and the coefficient parameters are processed according to the sampling rate. Rs The outputs are processed sequentially. Once all the filter coefficients have been output, the coefficient memory shuts down the output and releases the corresponding latches.

8. A digital transmitter for a spread spectrum communication system, characterized in that... The transmitter employs the digital interpolation shaping filter described in claim 4 for shaping filtering. The transmitter adjusts the spread spectrum clock to change the code rate of the spread spectrum code, so that the received code rate after the Doppler channel influence is within a preset difference range from the system design code rate. The digital interpolation shaping filter is designed according to the maximum code rate among the received code rates after the influence of the Doppler channel, and performs shaping filtering on the Doppler-compensated interpolated signal; then it is sent to the DA transmitter after up-conversion.

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